Method of making a garter-type axially resilient coiled spring

ABSTRACT

A garter-type axially resilient coil spring includes a plurality of coils canted along a centerline thereof with each coil having a trailing portion and leading portion. The disposition of the trailing portion is defined by a back angle between the trailing portion and a line normal to the centerline and the disposition of the leading portion is defined by a front angle between the leading portion and the normal line. Specific resilient performance, or load-deflection characteristics, of the spring is obtained by controlling the back angle. At selected back angles, the leading portion may be disposed at front angles beyond the range heretofore thought possible.

This application is a division of application Ser. No. 186,018 filedApr. 25, 1988, now U.S. Pat. No. 4,826,144.

The present invention generally relates to compression springs and, moreparticularly, relates to a method for making annular canted coiledsprings which exhibit preselected resilient, or load-deflection,characteristics, in response to axial loading of the springs. Thesesprings are also known as garter-type springs because of their shape.

As disclosed by Mather in U.S. Pat. Nos. 3,323,735 and 3,468,527,annular canted coil springs in many applications are superior toBelleville, wave washers, or coil helical compression springs, andgroups of compression springs arranged in a ring. This is particularlytrue for small springs in which the significant dimensions aresubstantially less than one inch.

The substantial number of different types of apparatus requiregarter-type springs, each having a specific load-deflectioncharacteristic required by the apparatus. Hence, careful design of eachgarter-type spring must be made in order to tailor the resilientcharacteristics thereof to meet the needs of the proposed application.For example, a spring designed for use in a seal, preferably has aworking deflection in which the spring provides a substantially even, orconstant, force over a broad range of deflection. With this resilientcharacteristic, variation in the distance between the seal members,which may be caused by wear, does not affect the spring applied sealingpressure therebetween. Other applications require that the springprovide a linearly increasing force in response to deflection throughouta specific operating range, while in some cases even a negativeload-deflection characteristic may be preferable.

Of particular importance are applications where the spring can maintaina predetermined load between untooled surfaces, which have greatertolerances, thus significantly reducing the cost of the unit through theuse of such untooled parts. This is of advantage in electricalcomponents, such as switches and the like.

The resilient characteristics of annular, or garter-type, springs, wasinvestigated by Mather and disclosed in the hereinabove referenced U.S.patents. Mather varied the ratio of the diameter of the coil to thediameter of the wire and, in addition, controlled the angle of slant ofthe coils. Mather found that the angle of slant determines the resilientand energy-storing capacity of the spring under axial load. In addition,Mather teaches specific slant angle, or profile angle, limitations inthe design of the annular springs.

It should be appreciated that while garter-type, or annular, springs, asa class, have the same general shape, wide performance variations existdepending upon the specific design of the spring. According to oneclassification, the annular spring may be either an axial load-bearingspring or a radial load-bearing spring.

As the classification implies, axial load-bearing springs are designedfor accommodating axial loading, while radial load-bearing springs aredesigned for accommodating radial loading. The hereinabove referred toU.S. patents to Mather are exemplary of axial loadbearing springs andU.S. Pat. No. 4,655,462 to Balsells discloses that annular, orgarter-type springs, may be designed for radial loading thereof.

The present invention represents a substantial improvement in the designof a garter-type axially loaded springs which provide for the tailoringof the resilient characteristics of the spring to a degree far beyondthat possible heretofore. While the springs of the present invention mayappear to be similar to prior art springs and their performancecomparable to other springs in many applications, their designcharacteristics can be controlled in order to enable the springsproduced in accordance with the method of the present invention to beused in applications not possible with heretofore annular springs.

For example, Mather in U.S. Pat. No. 3,468,527, primarily relies on thespring index which is the ratio of the diameter of the coil to thediameter of the wire to provide a means for adjusting the resilientcharacteristics of the spring. In U.S. Pat. No. 3,323,785, Matherteaches that a variation of its angle of slant α which is formed by theintersection of the planes containing the diameters of the individualcoils, with a plane normal to the axis of the coil, in order to alterthe resilient characteristics of the spring. This investigation foundthat springs could be made with the slant angles within the range of 35to 55 degrees, with an optimal angle of slant of about 45 degrees.

The method and spring of the present invention overcomes the hereinaboveidentified limitations regarding the slant angle α as defined by Matherand provides for spring designs which incorporates spring parametershereinbefore thought unworkable in view of the prior art.

SUMMARY OF THE INVENTION

In accordance with the present invention, a garter-type axial resilientcoiled spring includes a plurality of coils canted along a centerlinethereof. Back angle means are provided not only for defining thedisposition of a trailing portion of each coil with respect to a linenormal to the centerline, but also for determining the force-deflectioncharacteristics including the working resilient range of the garter-typeaxially resilient coil spring.

Heretofore, no one has recognized the importance of the spring backangle, hereinafter described in greater detail, and its dominant effecton spring performance. That is, by controlling the back angle, whichdefines the trailing portion of each coil, the resilient characteristicscan be designed to meet criteria heretofore not possible without thecontrol selection and adjustment of back angle.

Front angle means, hereinafter described in greater detail, are providedfor defining the disposition of a leading portion of each coil withrespect to the normal line. In each instance, the front angle means isgreater than the back angle means. Importantly, the front angle meansmay be less than 35 degrees, which is beyond the range taught by priorinvestigators.

The coils are interconnected in a manner forming a garter-type axiallyresilient coil spring with the trailing portion along an inside diameterof the garter-type axially resilient coil spring and the leading portionalong an outside diameter of the garter-type axially resilient coilspring.

More particularly, the garter-type axially resilient coil spring,according to the present invention, may include a plurality of coilswhich are canted in a clockwise direction. More specifically, the backangle may be greater than one degree and less than 35 degrees, with theback angle means defining a working deflection in which the garter-typeaxially resilient coil spring exerts a generally constant force in anaxial direction in response to the deflection of the garter-type axiallyresilient coil spring in the axial direction, with the workingdeflection being between about 10 percent and about 35 percentdeflection of the spring.

In accordance with the present invention, a method for making agarter-type axially resilient coil spring includes the steps of windinga metallic wire to produce coils canted with respect to a centerline ofthe garter-type axially resilient coil spring, with each coil having aleading portion and a trailing portion. The wire may be wound so thatthe leading portion is disposed to a line normal to the center-line ofthe garter-type axially resilient spring and the trailing portion isdisposed at a back angle to the normal line.

During winding of the wire, the magnitude of the back angle can beadjusted in order to achieve a preselected resiliency of the garter-typeaxially resilient coil spring. It should be appreciated that while theback angle is specifically controlled, the corresponding front angle mayvary depending on the coil spacing, that is, the average distancebetween the coils.

Thereafter, two ends of the wound wire are attached in a manner forminga garter-type axially resilient coil spring with a trailing portionalong the inside diameter of the garter-type axially resilient coilspring and the leading portion along an outside diameter of thegarter-type axially resilient coil spring.

More specifically, the wire may be wound in a clockwise direction andthe coils may be canted in a clockwise direction with regard to thecenterline. During winding of the coil, the back angle is adjusted todetermine the maximum mode and the total deflection load point of thegarter-type axially resilient coil spring, and the front angle may beheld constant while adjusting the back angle.

The back angle may be made greater than one degree and less than 35degrees, and the front angle may be made less than 35 degrees. In eachinstance, the front angle is always greater than the back angle of thespring.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will appear fromthe following description when considered in conjunction with theaccompanying drawings in which:

FIG. 1 is a theoretical load versus deflection curve illustrating thevarious parameters of an axially resilient coil spring;

FIGS. 2a and 2b are plan and side views, respectively, of a circularwelded clockwise spring, in accordance with the present invention, witha front angle on the outside of the spring and a back angle on theinside of the spring;

FIG. 3 is a load versus deflection curve for the springs shown in FIG. 2and identified in Table 1 herein;

FIG. 4 is a load versus deflection curve for a spring, in accordancewith the present invention, showing the characteristics of springshaving a front angle of less than 35 degrees and identified in Table 2herein;

FIGS. 5a and 5b are plan and side views of circular welded clockwise andcounterclockwise springs having the same physical dimensionsillustrating the difference in construction of springs having the backangle on the outside (FIG. 5a) and on the inside (5b);

FIG. 6 is a force versus deflection curve showing the resilientcharacteristics of the spring as shown in FIGS. 5a and 5b;

FIG. 7 is a depiction of winding a coil spring in accordance with themethod of the present invention; and

FIG. 8 shows the step of welding ends of the coil springs to form agarter-type spring.

DETAILED DESCRIPTION

Turning now to FIG. 1, there is shown an exemplary load deflection curve10, for the purpose of illustrating the characteristics of canted coilgarter-type axially resilient coil springs. As shown, when the load isaxially applied to the spring, the spring deflects in a generallylinearly fashion as shown, by the line in segment 12 until it reaches aminimum load point 14, which represents the point at which, after theinitial deflection, the load begins to remain relatively constant.

Between the minimum load point 14 and the maximum load point 16, theload deflection curved may be constant or show a slight increase asshown in FIG. 1.

The area between the minimum load point 14 and the maximum load point 16is known as the working deflection range. This spring is normally loadedfor operation within this range, as indicated by point 20, for a typicalspring utilized in conjunction with a seal, gasket, or the like, forsealing purposes. Loading of the spring beyond the maximum load point 16results in an abrupt deflection response until it reaches a butt point22, which results in a permanent set in the spring as a result ofoverloading. Also indicated in FIG. 1 is a total deflection range, whichis defined as a deflection between the unloaded spring and thedeflection of the maximum load point 16.

FIG. 2a shows a circular welded clockwise spring 30, in accordance withthe present invention, generally showing a plurality of coils 32, whichare canted in a clockwise direction along a centerline 34 thereof. Asmore clearly shown in 2b, each coil 32 includes a trailing portion 40and a leading portion 42, with the trailing portion having a back angle48 which provides for means for both defining the orientation of thetrailing portion 40 of each coil 32 with respect to a normal line 50 andfor determining the working resilient range of the spring 30 ashereinafter described in greater detail.

In addition, a front angle 54 provides the means for defining theorientation of the leading portion 42 of the coil 32 with respect to anormal line 50.

The spring 30 is formed by interconnecting the coils 32 in a mannerforming a garter-type axially resilient coil spring with the trailingportion 40 along an inside diameter 58 (see FIG. 2a) of the spring 30and a leading portion 42 along an outside diameter 60 of the spring 30.

As can be seen most clearly in FIG. 2B, the spring 30, in accordancewith the present invention, always has a leading portion 42 disposed ata front angle 54, which is greater than the back angle 48, defining thetrailing portion 40. That is, as the coil is traced in the circular-likemanner about the centerline 34, each revolution includes a trailingportion 40 and a leading portion 42, with the leading portion advancingmovement along the centerline 34 more than the advancement along thecenterline 34 when following the trailing portion 40 of the coil 32.

FIG. 3 shows force-deflection curves for springs, A, B and C, made inaccordance with the present invention, and having specifications setforth in Table 1.

FIG. 3 shows the wide variation in force-deflection characteristics forsprings made from the same wire diameter having the same spring insidediameter, the same coil height, with a constant front angle that can beobtained by a variation of the back angle 48. For illustration purposesonly, the front angle is held at 38 degrees, which is at about theminimum value taught by Mather for coil springs in U.S. Pat. No.3,323,785.

In general, Table 1, results are shown in FIG. 3, shows that the greaterthe spacing between the coils, the larger the deflection and the smallerthe back angle. The back angle exerts the greatest influence on thespring resilient characteristics and not the front angle, and thegreater the spacing between coils the greater the total deflection. Ascan be seen from FIG. 3, the force in the working deflection range ofspring B is substantially greater than that in spring C. Thischaracteristic is important when the springs are used in combinationwith a seal. Since the seals are generally made from a soft material,such as an elastomer or plastic, stress concentration is a primeconsideration and the lower the stress concentration, the longer thelife that can be effected on the seal.

                  TABLE 1                                                         ______________________________________                                              (d)             (D)               Coil-                                       Wire    Spring  Coil              Spac- Ra-                             Spring                                                                              Dia.    I.D.    Height                                                                              Back  Front ing   tio                             No.   (inch)  (inch)  (inch)                                                                              Angle Angle (inch)                                                                              D/d                             ______________________________________                                        A     .022    .840    .162  22°                                                                          38°                                                                          .018  7.36                            B     "       "       "     16.25°                                                                       38°                                                                          .033  "                               C     "       "       "     10.5°                                                                        38°                                                                          .044  "                               ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                              (D)               Coil                                        (d)     Spring  Coil              Spac- Ra-                             Spring                                                                              Wire    I.D.    Height                                                                              Back  Front ing   tio                             No.   Dia.    (inch)  (inch)                                                                              Angle Angle (inch)                                                                              D/d                             ______________________________________                                        D     .022    0.756   .162  9.25°                                                                        25°                                                                          .018  7.36                            E     .016    "       "     9.5°                                                                         21°                                                                          .016  10.125                          ______________________________________                                    

That is, because springs, in accordance with the present invention, canexert an equal force compared to prior art springs using smaller wirewith closer spaced coils, the stress concentration on cooperating sealmaterial is less. This results in more effective sealing and greaterseal life.

FIG. 4 shows the force-deflection curve for two springs made with thespecification set forth in Table 2. It should be noted that both ofthese springs are fabricated with front angles of 21 degrees and 25degrees, respectively, which is substantially less than the minimumangle set forth in the prior art.

FIG. 4 shows that the larger the wire diameter, the higher the force,compare spring D to spring E, and the larger the D/d ratio, the fasterthe minimum load point is reached. It should be appreciated that in thiscomparison the coil spacing is nearly the same between the two springs.While curves D and E may look considerably different, an analysis of thetwo shows that each of them have the same working deflection, that is,the percentage deflection between points 60 and 62 of curve D is thesame as the deflection between the points 64 and 66 of spring E.However, within this working deflection, the load is substantiallydifferent.

It should be appreciated then that the load characteristics and theworking deflection of spring E can be increased by increasing the numberof coils per inch, that is, decreasing the coil spacing. This providesfor substantially less stress concentration on a cooperating seal, notshown, as hereinbefore described.

It is important to distinguish the spring 30, in accordance with thepresent invention, from outside back angle canted coil springs, such asthose set forth, in companion U.S. patent application Ser. No. 186,016filed on Mar. 25, 1988.

FIG. 5a shows a spring 80 having a plurality of coils 82, with atrailing portion 84 and a leading portion 86, which are defined,respectively, by a back angle 90 and a front angle 92. The spring ofFIG. 5a represents a spring in which the back angle is along the outsidediameter 94 of the spring 80. This is to be compared with a spring 100shown in FIG. 5b, in accordance with the present invention, having coils102, with each coil having a trailing portion 104 and a leading portion106 disposed at a back angle 108 on the inside and a front angle 110 onthe outside, respectively. The spring 100, however, has the trailingportion 104 along an inside diameter 112 of the spring 100, and theleading portion 106 along an outside diameter 114 of the spring 100.

Although the springs 80 and 100 are made to the same dimensions, namely,an inside diameter of approximately 0.84 inches, a coil height(h) ofapproximately 0.162 inches, a coil spacing(s) of approximately 0.044inches, with wire having a diameter(d) 0.022 inches and each having aback angle of 14 degrees and a front angle of 25 degrees, theforce-deflection performance of each of the springs is entirelydifferent. This is illustrated in FIG. 6 which shows theforce-deflection characteristics of the spring in terms of thousands ofpounds versus the deflection of the coil in percent of the coil height.Curve F of FIG. 6 represents a performance of spring 80 while spring Grepresents a performance of spring 100. The two springs 80, 100 havealmost identical force-deflection characteristics in their workingdeflection range, however, the maximum load points have a variation ofabout 40 percent. Hence, it is preferable when a greater working rangeis desired to utilize a spring with the leading portion along theoutside diameter of the spring.

Turning to FIG. 7, there is shown a method for fabricating a garter-typeaxially resilient coil spring, in accordance with the present invention,by winding a wire 120 in a clockwise fashion as shown by the arrow 122about a mandrel 124. Alternatively, a wire 126 may be wound in acounterclockwise direction, as shown by arrow 128 about the mandrel 124.

It should be appreciated that the wire may be wound counterclockwise andclockwise and, accordingly, the coils may cant clockwise orcounterclockwise. In either case, the performance is the same as long asthe back angle is carefully controlled. For example, during the windingof the wire, the magnitude of the back angle is adjusted in order toachieve the preselected resiliency of the garter-type axially resilientcoil spring. Following the winding of the wire 120 or 126, the ends 130,132 of the wound wire are attached to form a garter-type axiallyresilient coil spring as shown in FIG. 2b, with the leading portion 106along the outside diameter 114 of the spring 100 and the trailingportion 104 along an inside diameter, 112 of the spring 100.

Although there has been hereinabove described a specific arrangement ofa coil spring, in accordance with the present invention, for the purposeof illustrating the manner in which the invention may be used toadvantage, it should be appreciated that the invention is not limitedthereto. Accordingly, any and all modifications, variations orequivalent arrangements, which may occur to those skilled in the art,should be considered to be within the scope of the invention, as definedin the appended claims.

What is claimed is:
 1. A method for making a garter-type axiallyresilient coiled spring comprising the steps of:fabricating by winding ametallic wire to produce coils canted with respect to a centerline ofthe garter-type axially resilient coiled spring, each coil having aleading portion and a trailing portion, said leading portion beingdisposed at a front angle in a range from 0 to 35 degrees with respectto a line normal to a centerline of the garter-type axially resilientcoiled spring and said trailing portion being disposed at a back angleto the normal line; during fabricating of the wire-adjusting themagnitude of the back angle in order to achieve a preselected resiliencyof the garter-type axially resilient coiled spring; and attaching twoends of the wound wire by welding in a manner that form forming agarter-type axially resilient coiled spring having the trailing portionalong the inside diameter of the garter-type axially resilient coiledspring and the leading portion along the outside diameter of thegarter-type axially resilient coiled spring.
 2. The method according toclaim 1 wherein the wire is fabricated in a clockwise direction and thecoils are canted in a clockwise direction with respect to thecenterline.
 3. The method according to claim 1 wherein the back angle isadjusted to determine the maximum load and the total deflection maximumload point of the garter-type axially resilient coiled spring.
 4. Themethod according to claim 1 the front angle is held constant whileadjusting the back angle.
 5. The method according to claim 1 wherein theback angle is made greater than one degree and less than 35 degrees. 6.The method according to claim 1 wherein the back angle is made to lessthan about 11 degrees.